The present invention relates generally to electroluminescent panels and deals more particularly with a method and related apparatus for continuous processing to produce large-scale foil-back electroluminescent lamp material. The invention further relates to split-electrode and parallel plate electroluminescent lamps and strip lamps made from the large-scale foil-back electroluminescent lamp material.
Lamps and processes for making individual lamps from electroluminescent material are known in the electroluminescent (EL) lamp art. Typical EL lamps are relatively small in illuminated surface area and are known as xe2x80x9cparallel plate lampsxe2x80x9d that are produced from a number of processes including screen-printing, lamination and other processes known in the EL lamp art. The generic construction of most EL lamps can be described as being built up layer-by-layer from the front substrate having: 1) a transparent front substrate; 2) a transparent conductive front electrode; 3) a phosphor/organic binder layer; 4) a barium titanate layer and 5) a rear electrode layer formed from a conductive coating such as nickel acrylic or conductive silver ink.
An alternate generic construction uses an aluminum foil substrate to form the rear electrode, in which case there is no front substrate because the lamp is built up layer-by-layer from the rear. Also, in the generic construction described above a portion of the front electrode is not coated with the phosphor/organic binder layer and is left exposed to permit attachment of an electrical connector to the front electrode. Inherently, clear conductors are fragile and cannot support connection and often a conductive ink, such as a silver ink, is used to support the termination and distribute the power applied thereto more evenly.
A disadvantage of EL lamps constructed as described above is the limited size or area that can be powered to maintain uniform brightness across the EL lamp. The transparent front electrode in these EL lamps is characteristically not a perfect conductor and exhibits a significant electrical resistance. This electrical resistance produces voltage drops that manifest as decreasing and lower relative brightness as the distance from the point of power connection increases. An EL lamp with a continuous silver conductor around its periphery is often used to obtain shorter connection distances to distribute current in a parallel plate EL lamp in an attempt to overcome the effects of voltage drops; however, the center of the EL lamp will become lower in brightness compared to the brightness at the periphery as the lamp area size increases.
D""Onofrio (U.S. Pat. No. 4,534,743) discloses a process for continuously manufacturing flexible electroluminescent lamps by applying the materials throughout the course of the process on a carrier strip, which carrier strip itself becomes part of the lamp and wherein the termination method does not use the front electrode. In the ""743 patent, the rear electrode is scored or xe2x80x9cscribedxe2x80x9d into two substantially equal areas so that the rear electrode areas are electrically isolated from each other. The terminations are then subsequently placed on the two rear electrode halves and connected to an AC voltage or power source. This type of construction is known as a xe2x80x9csplit-electrodexe2x80x9d EL lamp construction and the two rear electrode areas function electrically as a voltage divider, therefore twice the normal operating voltage is required compared to a xe2x80x9cparallel platexe2x80x9d EL lamp construction to achieve the equivalent brightness. The brightness, however, in a split-electrode EL lamp is obtained at a reduced current. The primary advantage of a split-electrode EL lamp compared to a parallel plate EL lamp is that most of the current, particularly for large surface area EL lamps, is distributed through the more conductive rear electrodes, which may be, for example, nickel acrylic paint or conductive silver ink. The front transparent electrode, typically indium tin oxide (ITO), carries a small amount of the current, which only powers a local region of the EL lamp. The xe2x80x9csplit electrodexe2x80x9d construction allows the fabrication of larger surface area EL lamps before any reduction in brightness occurs. A further advantage of the xe2x80x9csplit electrodexe2x80x9d construction is the ability to utilize higher volume and automated manufacturing techniques, particularly web-to-web processing, than would otherwise be possible with other EL lamp constructions which are built to a given specification provided beforehand. That is, continuous rolls of EL lamp material can be coated using standard converting equipment, which provides the advantage that the specific lamp size does not have to be predefined prior to the manufacturing of a roll of EL lamp material.
U.S. Pat. No. 5,019,748, assigned to the same assignee as the present invention, discloses a method for making an electroluminescent panel in a continuous fashion using a continuously moving carrier strip that becomes part of the electroluminescent panel or lamp to provide a highly reflective rear electrode that may be split in accordance with the xe2x80x9csplit-electrodexe2x80x9d construction techniques described in U.S. Pat. No. 4,534,743. The method described in the ""748 patent for making the electroluminescent panel includes depositing a reflective metallic layer on a smooth finished surface dielectric layer to provide a highly reflective rear electrode. The high reflectivity is a result of controlling the smoothness gloss of the second cured dielectric adhesive layer which causes significantly increased reflectivity of light from the rear to the front of the lamp in operation. The carrier strip can then be coiled after the lamp layers are formed thereon for subsequent payout in a production line that may, for example, die cut lamp shapes from the coil and split the rear electrode. Attachment of electrical conductors to the split rear electrode areas is then made for example, as disclosed in U.S. Pat. No. 5,045,755, assigned to the same assignee as the present invention. Although the ""748 patent describes a method for making an EL lamp using an ultraviolet (UV) curable binder and electrostatic deposition of phosphor particles to provide an EL lamp that is superior to the EL lamp production methods and EL lamps of the prior art, the lamp produced in accordance with the method of the ""748 patent is not entirely satisfactory. The EL lamp produced in accordance with the ""748 patent requires two separate coating and curing operations for the binder to encapsulate the phosphor particles, which are electrostatically deposited in a separate operation and a further third coating and curing operation to add a rear electrode. The structure thus produced is more costly than it need be resulting from the numerous separate operations required to produce the EL lamp material. Additionally, the EL lamp so manufactured has some performance limitations as well. These limitations may be manifested as lower total brightness resulting from a thick second binder coating and lack of rear barium titanate to impedance layer, and limited overall total size due to limited conductivity of the rear electrode.
Accordingly, it is an object of the present invention to reduce the cost of manufacturing EL lamp material by reducing the number of process steps in production.
It is a further object of the present invention to improve the performance of the EL lamp itself made from the EL lamp material by increasing its brightness and substantially removing limitations in the size or surface area of an EL lamp.
It is yet a further object of the present invention to provide apparatus for the continuous production of two primary substrates that are laminated together to create the large-scale foil-back EL lamp material in continuous rolls.
It is a still further object of the present invention to provide an improved foil-back EL lamp material and an EL lamp that reduces the time to make a product by eliminating registration and artwork requirements.
It is an additional object of the present invention to provide an EL lamp material that facilitates handling and is capable of xe2x80x9csplit-electrode,xe2x80x9d xe2x80x9cparallel plate,xe2x80x9d and xe2x80x9cspecial effectxe2x80x9d EL lamp construction.
It is a yet further object of the present invention to provide an EL lamp of a desired arbitrary size and shape to be cut from a continuous roll of EL lamp material.
In a broad aspect, the invention relates to a method for continuously manufacturing EL lamp material. The method includes coating an indium tin oxide polyester film (ITO/PET) substrate with a layer of phosphor particulate embedded in an organic binder defining a front substrate, coating an aluminum foil polyester film laminate with a layer of barium titanate defining a rear substrate, and then continuously laminating the front substrate and the rear substrate with the organic binder phosphor particulate layer facing the barium titanate layer to produce an EL lamp laminate material having an ITO front electrode and an aluminum foil rear electrode.
The method further includes coating the ITO surface of the ITO/PET substrate with a UV-curable organic binder prior to electrostatically depositing a layer of phosphor particulate on the UV-curable organic binder surface wherein the phosphor particulate is partially embedded in the organic binder. The UV-curable organic binder phosphor particulate layer is then set to a predetermined desired thickness.
The method further includes curing the UV-curable organic binder phosphor particulate layer prior to laminating the front and rear substrates.
The method further includes partially curing the UV-curable organic binder phosphor particulate layer prior to setting the thickness of the layer.
The method alternatively includes coating the ITO surface of the ITO/PET substrate with a slurry mixture of a UV-curable organic binder and phosphor particulate and then setting the thickness of the UV-curable organic binder and phosphor particulate layer to a predetermined desired thickness.
Further, the UV-curable organic binder phosphor particulate layer is cured prior to the step of laminating the front and rear substrates or the UV-curable organic binder phosphor particulate layer may be wet and cured after the step of laminating the front and rear substrates. Exposed portions of the phosphor particulate extending beyond the surface of the organic binder are fully covered and embedded in the barium titanate layer during the laminating process.
The thickness of the EL lamp laminate material is set to a predetermined desired thickness during lamination of the front and rear substrates.
The method alternatively includes coating the ITO surface of the ITO/PET substrate with a thermoplastic clear organic binder which is set to a predetermined desired thickness. The thermoplastic organic binder layer is warmed to soften it and then a layer of phosphor particulate is electrostatically deposited on the softened thermoplastic organic binder surface. The thermoplastic organic binder phosphor particulate layer is chilled to firm it on the ITO/PET substrate prior to laminating it with the rear substrate.
A further aspect of the invention relates to apparatus for continuously manufacturing EL lamp laminate material. The apparatus includes means for coating a continuous coil of an indium tin oxide polyester film (ITO/PET) substrate with a layer of an organic binder; means for depositing phosphor particulate on the organic binder, wherein the phosphor particulate organic binder coated ITO/PET substrate defines a front substrate; means for coating a continuous coil of an aluminum foil polyester film with a barium titanate layer, wherein the barium titanate coated aluminum foil polyester film defines a rear substrate; and means for laminating the front substrate and the rear substrate with the organic binder phosphor particulate layer facing the barium titanate layer to produce an EL lamp laminate material having an ITO front electrode and an aluminum foil rear electrode.
The ITO/PET coating means further includes a gravure roller for direct or indirect application of the organic binder layer to the ITO surface. The organic binder may be a UV-curable organic binder.
The phosphor particulate depositing means further includes electrostatic depositing means. A calender roll is used to set the thickness of the front substrate to a predetermined desired thickness.
Alternatively, the ITO/PET coating means may be a knife-over-roll apparatus for applying a slurry mixture of a UV-curable organic binder and phosphor particulate to the ITO surface.
The UV-organic binder curing means may be located prior to or after the laminating means. The laminating means includes a pressure-nip laminator or a heated-nip laminator.
A further aspect of the invention relates to a method for continuously manufacturing EL lamp material. The method includes providing a continuous roll of an indium tin oxide coated polyester film ITO/PET substrate of indeterminate length and width. The indium tin oxide surface of the ITO/PET substrate is coated with a UV-curable organic binder layer and a layer of phosphor particles is deposited in the UV-curable organic binder. The phosphor particle UV-curable organic binder layer is partially cured and set to a predetermined desired thickness. The UV-curable organic binder phosphor particle layer is cured, wherein the ITO/PET cured organic binder phosphor particle substrate defines a front electrode substrate. A continuous roll of an aluminum foil polyester film laminate of indeterminate length and having a width substantially equal to the width of the ITO/PET substrate has the aluminum foil surface coated with a barium titanate layer, wherein the barium titanate coated aluminum foil polyester film laminate defines a rear electrode laminate. The front electrode laminate and the rear electrode laminate are continuously joined with the organic binder phosphor particle layer facing the barium titanate layer to produce a continuous roll of EL lamp laminate material.
Further, foreign matter is removed from the indium tin oxide surface prior to coating with the UV-curable organic binder layer. The UV-curable organic binder layer is coated onto the indium tin oxide surface by direct or indirect gravure coating.
The UV-curable organic binder layer is coated with a thickness in the range of about 0.3 mils to 0.8 mils.
A layer of phosphor particles of like electrical polarity charge is electrostatically deposited onto the surface of the UV-curable organic binder layer and then discharged after being applied.
The phosphor particles deposited have a microencapsulated inorganic coating, preferably aluminum oxide. The thickness of the UV-curable organic binder phosphor particle layer is set by passing the partially cured organic binder phosphor particle coated ITO/PET substrate through at least one calender roll. The calender roll is heated to soften the partially cured organic binder to more easily reposition the phosphor particles.
Preferably, coating the UV-curable organic binder includes coating with a clear, UV-curable organic binder, wherein the organic binder is moisture resistant and has a dielectric constant in the range of about greater than 4, a dissipation factor in the range of about less than 0.125, and a dielectric strength in the range of about 1000+/xe2x88x92200 volts per mil.
The front and rear electrodes are continuously joined by passing the front and rear electrodes through a nip laminator, which may be a heated nip laminator.
Preferably, the rear electrode laminate is cut into pairs of parallel strips prior to continuous joining with the front electrode laminate to produce a continuous roll of split-electrode EL lamp laminate material.
A further aspect of the invention relates to an electroluminescent (EL) lamp material having a front electrode laminate comprising an indium tin oxide layer coated on a polyester film, an organic binder layer coated on the indium tin oxide layer and a layer of phosphor particles deposited on the organic binder layer; a rear electrode laminate comprising an aluminum foil polyester film and a barium titanate layer coated on the aluminum foil; and a laminate of the front electrode laminate and the rear electrode laminate with the organic binder layer facing the barium titanate layer to form the EL lamp laminate material. The organic binder is a UV-curable organic binder and the organic binder phosphor particle layer is set to a predetermined thickness prior to laminating the front and rear electrode laminates. The EL lamp material is cut to a desired arbitrary size and shape and further comprises the rear electrode cut to a predetermined depth through the aluminum foil polyester film and partially into the barium titanate layer to produce a split-electrode EL lamp having at least two electrically isolated rear electrode areas. Each of the at least two electrically isolated rear electrode areas have an electrical connector in contact with the aluminum foil for powering the EL lamp.
Preferably, the isolated rear electrode areas are of substantially equal area to emit light of substantially equal brightness and are of unequal area to emit light of unequal brightness. The rear electrode may have multiple pairs of rear electrode areas for special effect lighting.
Alternatively, the EL lamp material is cut to a desired arbitrary size and shape and further comprises the laminate having dual scribe lines along a marginal peripheral region cut to predetermined depths through the laminate, wherein the first of the dual scribe lines is outward of the dual scribe lines and is cut completely through the rear electrode laminate and the phosphor particle organic binder layer terminating at the indium tin oxide layer, and the second of the dual scribe lines is cut to a predetermined depth through the aluminum foil polyester film and partially into the barium titanate layer to produce a parallel-plate EL lamp.
Preferably, the laminate region between the first scribe line and the laminate outer peripheral edge further includes an electrical connector through the laminate and in electrical contact with the indium tin oxide for powering the front electrode defining one plate of the parallel plate EL lamp.
Preferably, the laminate region between the second scribe line and the laminate outer peripheral edge opposite the laminate outer peripheral edge outward of the first scribe line further includes an electrical connector through the laminate and in electrical contact with the aluminum foil for powering the rear electrode defining the other plate of the parallel plate EL lamp.
Preferably, the first scribe line is flooded with a conductive material.